It's an awesome game. You can try out one of the early versions for free. Just download them from the website. I'm not sure how good these versions are. Currently you have no financial limitations or reentry physics (apart from components falling off). I have managed to put two satellites in orbit and a one manned orbiter has returned safely. One stuck in orbit and onther stuck in an orbit around the sun. Luckely the Kerbals don't seem to require food or air.

So what's Kerbal Space Program like? I had a look at it early on in development and seemed pretty cool.

This post was mostly for XP btw :P